Towing Mods: how hot can we safely get a D24T?
 

In one month I'm towing a 3,000lb Catalina 22 sailboat over the infamous "grapevine" mountain pass in southern california, with a peak altitude of 4,160 ft. My goal is to prepare my 1984 760 diesel in advance such that my engine survives this difficult task. My brakes and suspension are already heavily upgraded, so I'm *only* worried about engine cooling issues here. The boat trailer also has excellent and brand new brakes. The car is also factory rated for towing this weight.

Anchored off Santa Cruz Island this January, after towing to the launch ramp with a 740 Turbo:
http://d24t.com/attachment.php?attac...1&d=1374605491

Goals
-calculate EXACTLY how hot she can run, and monitor closely such that I pull over before damage occurs
-modify the car to maximize the margin of safety
-plan a safe driving strategy
-have an awesome trip sailing with my dad in the California Delta

Engineering starting premise
The engine will be fine as long as the coolant remains in the liquid state. Therefore, I will estimate as accurately as possible the true boiling point, and not allow the engine to get within 5 degrees Celsius of this value.

Please no comments about how I'm "over-thinking this." I'm an engineer, and I enjoy solving problems this way.

Cooling concentration and pressure considerations

I tested my cooling system for pressure handling with a bicycle pump, and tested the concentration of antifreeze with a float hydrometer.

It turns out the cap is opening at 10psi, and I'm at 30% antifreeze. Both are way below spec. My Zerex g-05 ethylene glycol based coolant is rated to boil at 128C with 15psi of head pressure at a 50/50 ratio.

To raise the concentration, I'm going to replace coolant with pure antifreeze according to this formula:

(0.3(3-a)+a)/3=0.5
where a = antifreeze volume replacing current fluid
0.3 = current concentration
3 gal = system volume
0.5 = desired concentration

This suggests I need to replace 0.86 gallons of coolant with pure antifreeze to get up to a 50% mixture. To raise the opening pressure, I ordered a new 16psi radiator cap.

I will also be cleaning out the radiator with degreaser, as my radiator is still clogged with oil from the oil cooler blowing. I'll also be adding a VERY VERY large external oil cooler using aircraft grade hardware.

I still need to open up some basic chemistry textbooks to estimate my final boiling point. I'll be using a 16 psi radiator cap, but on the mountain pass at 4,160 ft I'll be at 12.7 psi ambient pressure (2.1psi below sea level pressure) so I need to consider this factor as well. I'm guessing the boiling point will be somewhere around 125C, allowing me to safely run up to 120C.

Edit: Boiling point estimate
Based on this PDF, a good rule of thumb is that 1 psi of pressure raises the boiling point by 3 degrees F. Therefore, based on my coolant specs I expect my boiling point will be about 127C at 4,160 ft with a 16psi cap and a 50/50 mixture. Therefore, I can safely run up to 122C, and will set an audible alarm at 120C for the climb.

Driving Plan

I'll try to hit the pass at the coldest possible time, which should also have the least traffic. This means hitting the summit right before sunrise, which means between 5am and 6am where it should be under 70F even on the hottest august days.

In a reply on my "Ebay radiator" post, 745turbogreasel said to us 1/4 box of Cascade dishwashing detergent to clean out the radiator. I had used Tide in the past on my 1957 Mercedes 180D and it worked fairly well. It did take several flushes with clean water to get all the soap out. I removed the thermostat to make sure the flow was good.

The oil cooler is an excellent idea. I put a small Volvo turbo oil cooler on, using the Volvo sandwich plate attached below the oil to water cooler so I get the benefit of the heat exchanger plus the air to oil cooler.

I'm thinking if this engine can pull a Pinzgauer it can handle the boat.

I already flushed about 10 times with laundry soap, and it now drains clear... but it seems to mysteriously still run warmer than before! It's a 11 month old Nissens radiator. I'm going to try removing it from the car, and soaking internally with purple degreaser as commonly done with Volvo intercoolers. I'll also be cleaning out a used mid-90s Volvo intercooler to install at the same time.

Any idea what those things weigh? I'd imagine the Pinz has lower gears and a vastly superior cooling system. I've come to the conclusion that the D24T Volvo cooling system is crappy for some reason, because it runs much hotter uphill yet makes much less horsepower than the Volvo red block engines in the same car. Maybe the red blocks flow water at a higher rate or something. Even with a brand new radiator, tropical fan clutch, new thermostat, and cast iron water pump I can hit 116C uphill with my D24T. A stock red block turbo making 50% more horsepower with a smaller radiator and a less efficient engine would never get over 100C under the same conditions. The same tropical fan clutch also kicks in at much lower temps on the red block despite the same thermostat opening temps, suggesting much better heat transfer to the radiator in the red block.

Any pics of your car? The ponton is one of my favorite cars, I've always wanted one!

I find if I drive to keep the EGT below 1250, the temp behaves quite nicely no matter how long a hill I'm pulling.

IMO gauge sender placement and something in the design not allowing the head to reject heat fast enough are working against us.I think having the cooling system configured in such a way as to have a constant out flow at the back of the head may help.

As far as the car half of the cooling system, it's the same as a 960 which works great, even with a v8.

Meth injection to keep EGT down might be an effective approach.

Interesting, I've had an EGT gauge installed for years but haven't drilled and tapped for the sensor. I'll go ahead and do that this weekend. Is a metal plate over the EGR port an okay mount location?

My temp sensor is actually an aftermarket digital one mounted to a vacuum pump bolt. My handheld infared thermometer says that the head has relatively uniform temps, always at the same level as what the digital one on the vacuum pump bolt reads.

1957 Mercedes 180D pictures.
 

The 180D is the first diesel I started working on about 7 years ago and it's the one that got me hooked on diesels.

I only have a few pictures of this car but it gives you an idea of the before and after. It's not perfect but it's my daily driver and is perfect for getting around town and for short trips around Reno. I have driven it over Donner Pass on I-80 to Sacramento and it never went slower than 50 mph in the steepest sections. On flat ground I can run 65 - 70 mph all day long!!

http://i1180.photobucket.com/albums/...dwithRiley.jpg

http://i1180.photobucket.com/albums/...ps6899d705.jpg

Beautiful. I think it's a close tie between a matte black Ponton and the 300 Adenauer for classiest looking car ever made. In my book, yours wins since it's also diesel. The performance doesn't sound too bad either, it's a rocketship compared to my Isuzu Trooper which takes similar passes at only 25mph. I've done Donner Pass only once, in a 1983 760 Diesel but remember that it was formidable- very steep and high altitude.

If you ever want to sell it contact me!

I'd think so, but I used a non EGR manifold.
20 minutes well spent for sure, it helps you track heat generation and economy in real time.

Cool lookin 180D. I pictured it black also. Back to EGT tho. Is the best place to put the egt probe in the collector for the turbo?

yes

Here is mine, but you don't really need to remove the manifold .
http://i18.photobucket.com/albums/b1...Picture028.jpg

The oil cooler parts arrived and are ready for a weekend install project! Now I need to learn how to assemble braided stainless lines.

http://d24t.com/attachment.php?attac...1&d=1374934240

The oil cooler is installed!

Installing AN braided steel fittings was super easy- way easier than I expected. I just took it on a test drive in heavy traffic with the A/C running and it stayed under 90C, but it's hard to tell how it would be on a hill climb.

I was very careful to route the hose so that there is zero chance of chafing, and with strain supports for the oil cooler. Hopefully this system will be more reliable than the factory oil cooler.
http://d24t.com/attachment.php?attac...1&d=1374974843
http://d24t.com/attachment.php?attac...1&d=1374974843

That is a massive oil cooler!!!! It looks good, and the mounting of the hoses looks good.

Thanks! It's probably an overkill, but it's really intended to cool the engine itself rather than just the oil.

I'm convinced that the D24T doesn't need an oil cooler to keep oil temps low enough with good synthetic oil, but Wren Wright on the D24 e-mail list suggested this as a method to increase the overall cooling capacity of the engine.

I've not fitted an EGT gauge to mine, just because I don't want to take the manifold off.

If you were to drill and tap the manifold without removing it, wouldn't you just get metal swarf in the turbo?

After pulling the radiator, I found it still clogged with oil six months after extensive cleaning!

So I soaked it with purple degreaser for an hour, reinstalled, and did TurboGreasel's electrasol flush TWICE. Hopefully it's clean now.

I also added an OEM 1992+ intercooler while retaining the factory A/C (which still blows cold). I had to remove the pusher fan to make room, and move the A/C condenser down and forward while fabricating new brackets (the condenser now bolts to the intercooler like 92+ cars). Also had to cut and grind on the car with the dremel for a solid day to make everything fit. I think this only fits because I have a newer NISSENS radiator which has intercooler piping cutouts on the end tanks.

http://d24t.com/attachment.php?attac...1&d=1376486527

I still need to plumb the intercooler in, coming soon! The plumbing will be VERY tight on the passenger (right) side, I'll probably need to re-clock the turbo, and cut part of the airbox away.

Also, the A/C condenser is now in the way of the hood cable- I added some rubber hose guides for now but will soon fabricate a new cable from a bicycle brake cable kit to route it around the condenser.

Anyone know if the plastic "wind guides" between the radiator and bumper do anything useful? I had to pull it to fit all this crap in there, but I could probably get it back in with some careful cutting and Turbobricks style "zip-tie sewing."

I think they are a part of the equation, but the ones from a newer car might just fit.
Did you have to do much trimming on the uprights by the radiator? I got a rad cradle off a 93+ to put that style intercooler in my car, but I think I am going with an China Xtreme Racing IC instead.

I had to cut out an opening for each of the intercooler outlets- a section of sheet metal about 5"x3". My tiny cordless dremel managed in little bits over two days with long cool down periods...

The appeal to me is that this already has an engineered mounting system for the 7/9 series... although that might be overrated because I had to do a lot of cutting, bending, and trimming to make everything actually fit.

Hey Tyler, how're the towing modifications going? I think you're close to leaving for your trip ... if you haven't already. :eek:

These may be too late to count now, but a few suggestions in case:

- Low gear, elevated engine speed, light load, low EGT are the best recipe for keeping cylinder head temperatures under control. I drove my 745 TD over the Grapevine last July, did it around midnight, took it easy and had no problems. I found later in that same trip climbing up other passes that I could make the needle start to climb by selecting a higher gear and putting my foot down further to maintain the same speed. 3rd gear at around 3200-3500 rpm with no more than 3-4 psi of boost on the gauge kept it in check even when ambient temps were over 105F. Pushing any more than that in those circumstances led to issues.

- Cooler thermostat is a huge factor and adds greatly to thermal stability and engine's ability to exhaust heat. 80C Wahler t-stat, part # 035 121 113, is the best one and makes a major difference in engine's ability to transfer heat to the rad.

- I think your premise that the engine will not suffer as long as the coolant does not vaporize is flawed. I think devoting a lot of energy to knowing exactly how hot it the motor is and how hot it is able to get so that you can run as close to that threshold as possible is also not a great approach. For one, we don't know 100% that the head can't be damaged as long as the coolant is liquid. We do know that the head doesn't like to get much hotter than normal operating temp and that headgasket failure threshold conditions are unusually easy to achieve with this engine, relative to others. For another, your ability to really know cyl head temps is limited since you're only measuring at one (stock) or at most a few points -- temp could be higher elsewhere, up to and beyond the boiling point, even while according to your measurements you're maintaining a >5C distance from your calculated limit value. Your decisions could be affected by incomplete or inaccurate information, and something unexpected might happen at a point you thought would be safe. Also in terms of unexpected happenings, to keep the coolant liquid requires running system pressure as high as possible, which involves increased risk of a component rupturing. Combine the intention to run the motor at temperatures well in excess of target normal operating temp -- leaving a limited cushion for reaction if something happens that causes temps to suddenly rise further -- with the necessity of high pressure and its affiliated risks, and you are inviting sudden disaster in a big way.

On that point, don't forget too that even if your information is perfect in terms of accuracy and resolution (which it cannot be), when you're on the highway with traffic nearby, a situation could start to develop and your ability to respond to it might be limited by the circumstances around you. If you're going to run close to the edge and leave yourself very little time between the point when the alarm bells go off and when the situation gets out of control, then you'll be putting yourself in a position where you might have to make the decision to sacrifice the motor in order to avoid an accident, which would be a shame. In a laboratory sense it's a cool idea to push the absolute limits but your environment in this case will not be especially well controlled. I share the interest in experimentation, but if you're hoping to have the car survive this one, then rather than approaching it with the goal of running right on the line between hot and too-hot and trying to marshal sufficiently precise information to know exactly where that is, I would focus instead on trying to maximize the safety margin by aiming to keep it as cool as possible. The safety of car and passengers/other drivers alike (as well as the success of the trip, of course...) hinges on having maximum time to react to any signs of trouble and aiming to back off well *before* your situation starts edging towards the danger zone.

I usually operate with the assumption that anything outside the range of normal operating temp (i.e. exact middle on the gauge -- let's say up to 100C) is not safe for the motor. With that strategy I've driven mine on trips through the western US under many different weather and terrain conditions, usually with success -- but not always, even using this very conservative approach. :eek: The margin is pretty slim and what's only a little too warm in something else can be way too warm in one of these. I think they're completely solid as long as you keep the temps absolutely in check, but you have almost no headroom to play with. My sense is that 120C as an alarm point could be already way past the point of no return -- I'd be backing way off way before then -- but I'll be interested to hear what happens....

I leave in 2 days (sunday morning). My planned car modifications are done so I'm focusing on putting brand new brakes and wheel bearings on the trailer.

Great advice, this is a lot of good stuff for me to consider, and it did come in time. I always appreciate your advice, I recently purchased a 2001 golf TDI for my wife, and reading everything you wrote in the past about the 01m was very helpful.

The relationship between EGTs and engine temps isn't something I thought about a lot before, but I can see how that will be critical. I will definitely use the high rpm/low throttle technique. In the past I have always used full throttle up grades.

Why is the 80C better than the 87C? Won't they both be full open all the time up a grade? I currently have a brand new 80C BEHR, and a brand new 87C Wahler but was planning to go with the 87C Wahler. Should I put the 80C BEHR in instead?

I haven't collected a lot of data, but it seems my fuel economy has been much better in the past with an 87C vs 80C thermostat.

That is a good point. I do have a very accurate digital temp gauge mounted to the head itself, and I've found with my infared thermometer that this usually represents the highest temp I can find on the exterior of the motor. However, I suppose I shouldn't expect the hottest part of the motor to be the exterior surface!

I agree with you, but in that case the D24T may not be suitable for towing at all. On other motors (such as Volvo red blocks) a good condition cooling system will never let the motor exceed 100C.

My experience with D24Ts is that they can't even get the fan clutch to engage solid until about 110C, and aren't seriously throwing off heat until close to 120C. Hopefully that will change now with my giant oil cooler, and 100% dialed in cooling system. I've done some full throttle runs up long grades without a trailer but with the A/C on in over 100F heat, and I currently can get it just to 100C but no hotter.

Before my cooling system improvements I have ran this motor to 118C without problems, but I may have been pushing my luck.

Per your advice, I will (instead of pushing the limits) go as slow as I possibly can, and stop as often as possible to let it cool. I will be going on a Sunday morning before sunrise, so I should have virtually zero traffic. Climbing at very low speeds in the rightmost lane is considered acceptable anyway on the grapevine.

I have blown head gaskets twice in the past on D24s, but both times there was a total loss of coolant, rather than simply getting warm with the coolant remaining liquid... and both motors had fiber gaskets. My current motor has an MLS gasket, and also has a giant 1.5 gallon coolant reservoir with a float sensor in the very top of the range.

Here is the elevation profile for my upcoming trip:

http://i.imgur.com/L7CQAGy.png

The grapevine is steep but once I pass that it's nearly flat. Also I'll only be going north where the uphill is less steep. I'm not too worried about the downhill, as I'll go very slow at high RPM and likely won't even need to use the cars (brand new) braking system. The braking system on the trailer is also brand new and rated for about twice the weight it will be controlling... and most importantly everything has brand new high boiling point fluid.

Dont rev so slow as to bog on shifts, struggling to regain speed makes as much heat for much longer than a higher RPM pull and a smooth shift. Make the most of your inertia.
CA 17 I can pull in 5th, 3000-3400 even on a pretty hot day. If I get blocked, I have to be careful getting back up to that speed, even on a much cooler day, and ike I said earlier, as long as my EGTs are under 1200, never a problem.
My fan mostly seem s to kick in before the gauge starts to rise, I feel it about 1/8 mile(I think) into most of the steeper high speed hills here, pretty distinctly drop maybe 5HP.

Almost ready...

http://d24t.com/attachment.php?attac...1&d=1377356595

I definitely advocate for the 80C t-stat over the 87. When combined with a healthy radiator, in my experience this seems to resolve or improve a great majority of the serious issues with the way the D24 cooling system operates in conditions of heavy loads and high temps. I'll give some of my theorized reasons for this when I have more time, but I wanted to post this while you still have time to put the t-stat in. Suffice for now to say that whatever theoretical ideas I have about this are things I have tried to come up with, after experiencing the results, to explain the *reality* that it does help, rather than the other way around.

The Behr should be equal to the Wahler in quality -- I'd put it in there and carefully make sure you get all the air bled out!

Want to absolutely avoid full throttle and boost for sure. As 745TG said and I have also experienced, you can cruise at moderate steady-state load safely for a long time... but if you spike the load and EGT suddenly it can make a big difference in engine temp even if only for a few moments. If your strategy is high gear and full throttle up a grade then I'm not surprised you're accustomed to watching the temp gauge rise routinely. I'd aim for a balance point that lets you stay on the road but keeps gauge in the dead middle, and plan to back off as soon as it starts to rise, if you want the most conservative possible approach.

It's no problem to blow the gasket on a motor that still is full of coolant... ask me how I know. Get it hot enough where the head starts warping or the bolts stretch and you're there -- you start with a small combustion gas leak and pretty soon after that the motor suddenly shoves about 3 gallons of coolant out the top of the expansion tank -- game over. Doesn't help that the hotter the motor gets, the less ignition delay there is after start of injection, so you effectively get a little more timing advance when you're approaching the limits for heat -- increasing peak combustion chamber pressures and making gasket failure all the more likely. The MLS gasket is not indestructible either; I have had to replace them before. Doesn't change the rules in terms of what is acceptable and what is too hot, only means that it's not subject to failure just by being in the motor long enough to erode from normal use. ;)

I installed the 80C BEHR even though I can't think of a reasonable mechanism by which it could help. At this point I'd resort to anything that might give me a better chance. As an engineer I know theories are usually missing critical details about reality.

My usual strategy is high rpms + full throttle... this is a pretty under-powered car by modern standards and that's what it takes to keep up with traffic and keep my wife from asking me to buy a faster car. I typically drive hard and keep it over 3,000rpm. My feelings are that a properly built and maintained car should easily maintain 100% engine output without overheating... and if a car can't it's cooling system needs to be significantly upgraded.

However, tomorrow morning I'll be shooting for 4000rpm in 1st gear with light throttle if I can manage it safely traffic wise, although I probably have enough power and cooling to do the climb in 2nd.

If you see this soon enough, what are your thoughts on the altitude compensation system on the injector pump? I'll be going high enough to trigger it, and it's operational still. If advanced timing with a hot engine is a problem should I bypass it? My timing is set to the factory 0.85mm.

1st gear is pretty short. I'll wager you will do OK in 2nd or perhaps even 3rd on flatter stretches depending on how it seems to do and how warm it is outside. I don't know whether going up to really high sustained engine speeds will help or be detrimental. I think the reason somewhat elevated revs help is that you can keep the car moving while keeping the load on the motor light, and simultaneously spinning the water pump and fan at a good rate of speed -- I think you achieve those things satisfactorily by about 3000 rpm. Going further beyond that I think the goal is vehicle speed more than cooling effect, assuming you can do it without making boost and EGT rise significantly. My non-scientific sense is that around 3300-3500 is a good spot, or at least that seems to be where mine was happy; much above that, it gets difficult to keep boost down and also you're getting into an inefficient combustion range where to my mind it seems possible that heat rejection per unit of power produced might be greater than it is in the midrange. That's a conjecture, though; I'll be interested to hear your results if you try spinning it faster. :)

Dunno, I generally run mine with the wires jumpered at the barometric switch to keep the system from engaging, but I also run more static timing than you do (~0.95mm). I don't think we have a way of quantifying how much advance that system adds in terms of mm of plunger travel at TDC; however, I got to be present while a D24T VE pump was being run on a calibration bench recently and watch the various timing advance mechanisms in action, and we concluded that the altitude compensation solenoid adds about a degree at low rpm and a degree and a half in the upper end. Hard to reach any concrete conclusions without seeing a lot of engineering data about how combustion temps and actual start of ignition are affected in this engine by the combined factors of altitude, ambient temp, engine temp, and start-of-injection timing, but my tentative hypothesis would be that at the timing setting you are running and the way you're planning to drive it, it won't make much difference whether it's engaged or not. In high-load situations where the duration of the injection events is relatively long, insufficient timing advance can significantly increase EGT, so if you were going to be hammering it up the hill then you'd probably want to be sure it was connected and working, but since you're not planning to be leadfooting it that effect probably will not be a major factor. I would probably leave it connected and see what happens when you cross 3000' or wherever it kicks off -- maybe make a little jumper wire so you can disable it quickly by the roadside if you don't like what it does?

Makes us begin to appreciate the challenge that Bosch/VAG had in tuning these mechanical VE pumps to perform under varying conditions... why the TDI was such a huge step forward. Everyone that builds "m-TDIs" with mechanical pumps, I can never understand -- I guess they assume the direct injection is the main advantage they have, but I think their electronic feedback control is at least as important in making them run as well as they do. :rolleyes:

Good luck! Objectively speaking attempting this with a 30yo car known for cooling system trouble and fragile cylinder head is nuts -- hopefully you're well aware of that -- but it sounds like you could succeed in making it work out. Let us know how it goes. :D

I had heard that in its day, it was the best-performing diesel passenger car. Shows how much progress has occurred.

The 524TD will give you a run for the money, but no wagon option here anyway.

Here's some data from the "SAE paper 790206" - "New 5- and 6-Cylinder VW Diesel Engines for Passenger Cars and Light Duty Trucks" paper published in March 1979.

"The ratio between crankshaft and water-pump speed was raised to i = 1.1 (i = 0.85 in the gasoline engine). This results in a cooling water flow of between 140 and 170 liters per minute at rated speed, depending on the cooling-system flow resistance curve." (converts to 37 to 45 gallons per minute!)

That sounds like a lot of water moving through the engine.

My observation of the importance of a GOOD working thermostat is that when the engine is warmed up the back end of the thermostat must close the flow coming out of the block in the position right behind the thermostat, thus forcing all the fluid flow either out the back of the block or up through the water outlet on the head. The suggestion to use an 80C thermostat is probably a good idea since it opens sooner and thus closes that water flow coming out of the block.

It is probably a good idea when driving under a heavy load to turn on the heater to allow more water out the back of the head. My concern is there's not enough flow at that end of the engine, ie. in and around the head and cylinders at #'s 5 and 6. It may not make much of a difference but I like the idea!

So,me head gaskets are missing a row of 'steam holes', I wonder about adding one in the back(or more) .
Also a bypass heater valve(90s Ranger, Caprice)could give more outflow at the back, especially if you've removed the water-oil cooler.

Any idea what 'rated speed' is?

Heat
 

Cook YOUR head instead of warping aluminium! Ask me how I know... Many, many times I saved car(s) and myself too by turning the heat on, full blast; it definitely does help a lot!
Especially because you can never really truly know how close you already got to the edge of a later serious & irreversible overheating. Yesterday I PM-d him about it and I hope he got the message in time before his departure...
Let me off-topic a little: We used to have a unique Volga wagon pimped with the 6 cyl PRV engine that was one unreliable engine, needing so many things fixed all times, and that car was slightly overheating all the time, ate a couple of headgaskets but turning the heat on always worked for years to get around town... long story from around 1978-1989. RIP, he rusted away since then, I`m sure. My Dad might be driving it in Heaven...
Heat up, open the sunroof.

In 1980
 

Yes, the 524td was indeed a big thing those times. Although in late 70`s & early 80`s Europe already had nice diesel options with relatively reliable, low-maintenance engines. That time most of them were considered `luxury` cars... I grew up In Europe and I can tell, it was (is) something hard to get for average people... Renault, Peugeot, Audi, Bmw, Mercedes; just to name a few. My all time favourite I think stays the same for now, the d24t & the W123 MB series. Nowdays, Europe has a huge amount of diesels rocking all over the roads and almost every car manufacturer has *multiple diesel options... for example Skoda (Vw of course :)
This tear sheet is from a 1980 US magazine.

Heater valve always open EXCEPT during max A/C. But arranging the controls for heat & max fan would maximize airflow thru the heater core, pulling more heat out of the engine and onto your feet!:)

http://images.apwcontent.com/is/imag...?$APW_imgProd$Not sure if this one is the right way to 'hot' but you get the idea

I made it no problem! I was so excited I yelled in joy when I hit the summit! Thanks for all the help and advice, I couldn't have done this without you guys. Now I get to spend a week sailing in the California Delta w/ my dad.

I climbed the grapevine at 3000-3500 rpm in 3rd gear most of the way, going down to second on the steepest bits. Peak temp was 102C when I floored it, but I could keep it under 100C. That's compared to 116C with no trailer last time I drove the same road. I think my cooling system can handle continuous full load at low speed without overheating.

After the grapevine, I was able to maintain 60mph in 4th gear, running the A/C and cruise control all the way to Sacramento and the engine stayed cool. I also never had to downshift once after getting past the grapevine. I was far from the slowest vehicle on the road. Once the weather got hot around noon power reduced a bit, and my speed dropped to 57mph.

Also, coming down the grapevine I didn't touch the brakes the whole way. With the A/C on at 3,000 rpm the D24T had enough engine braking to keep the speed constant. The brakes were cool to the touch at the bottom of the grade.